Mixed-Valence Cyanopyridine-Bridged Complexes of Pentacyanoferrate and Pentaammineruthenium: Electronic Structure, Stability, and Redox Reactivity

Abstract

The mixed-valence binuclear complexes, [(NC)5Fe(pyCN)Ru(NH3)5]n (4- and 3-cyanopyridine isomers, with nitrile-N and pyridine-N binding to Ru and Fe, respectively) were prepared as solid compounds through stoichiometric oxidation of the fully reduced (II,II) binuclear complexes, R, with peroxydisulfate. By analysis of IR spectra, the solids were observed to be a mixture of the predominant electronic isomers with a FeII, RuIII distribution, with minor amounts of the FeIII, RuII isomers. In aqueous solution, R was oxidized with peroxydisulfate to M, the mixed-valence complex, and to Ox, the fully oxidized complex. The M complex shows an intervalence band at 938 nm; by application of the Hush model, it is described as a valence-trapped RuII, FeIII complex; the latter electronic distribution is supported by UV−visible, electrochemical, and kinetic data, but a minor amount of the isomer with a FeII, RuIII distribution is also present in the equilibrium. The M complex is unstable toward dissociation and further ...